1. Field of the Invention
The present invention relates to a method for installing a utility pole and an arch-type underbracing by using an extendable excavating unit mounted on an auger crane, more particularly, two steps of excavation process is carried out for a excavating point to erect the utility pole and install the arch-type underbracing under the ground at a same time at the construction site.
2. Description of the Related Art
The methods for installing utility pole underbracing include construction by manual labor and mechanized methods using a backhoe or auger crane.
Of these, utility pole construction work using an auger crane can be said to be the most universal construction method. To take a look at this method, an auger crane is used to excavate to the insertion depth, which is about ⅙ of the total pole length depending on the length of the utility pole, not exceeding 2.5 m, and the utility pole is inserted and erected in the excavated pit. After that, in order to install a rectangular utility pole underbracing, construction is carried out in a sequence of processes of additional excavation by backhoe or manual labor to make insertion of a rectangular utility pole underbracing possible, installation of the rectangular utility pole underbracing, and backfilling of the pit.
The utility pole underbracing work including installation of the utility pole underbracing, earth work which is carried out in some cases and its execution process will be described in more detail.
First, as shown in FIG. 1A, an earth wire 101 is put into the inside of the utility pole 100, and with the earth wire 101 drawn out from the lower end portion of the utility pole 100, a pit 102 is excavated at the location where the utility pole 100 is to be erected. Next, the utility pole 100 stands upright with the earth wire 101 drawn out onto the ground surface to prevent it from going into the pit 102. At this time, the earthing resistance base value, kind of soil and site conditions are considered before deciding the construction method, excavation method, excavation area, and excavation length, etc.
With such conditions considered, an earthing copper rod 103 having an iron pin is struck and driven into the pit 102, as shown in FIG. 1B. To install the earthing copper rod 103 in series, after the first copper rod goes down to the floor of the excavated pit 102, the iron pin is drawn out and the earthing copper rod 103 is connected in series. Next, the iron pin is assembled to the end of the second earthing rod and struck again to drive it in.
Especially, when the second earthing copper rod goes down close to the excavation floor, the earthing resistance is measured. At this time, if the earthing resistance is below the specified value, the iron pin is drawn out, the lead terminal inserted, and then the earthing copper rod is struck to drive it in completely.
As for the method of installing earthing electrodes, series installation by the deep strike method is advantageous as shown in FIG. 1C. In the case of a reinforced concrete utility pole, the earthing copper rod 103 should not be in direct contact with the utility pole 100, and in the case of a steel pipe utility pole, the earthing copper rod 103 is to be earthed with a separation of 1.0 m or more. In the case of installing the earthing electrodes in parallel, it is preferable to install them with proper spacing between earthing electrodes according to site conditions.
After connecting and compressing the earthing wire 101 and the lead terminals of the earthing copper rod 103 by the earthing sleeve, the pit 102 is backfilled and tamped to complete utility pole construction work.
However, in the utility pole construction work as mentioned above, the earthing resistance base value, kind of soil, and site conditions, etc. should be considered for the method of setting the earthing resistance using earthing copper rods before carrying out the work. Besides, since there are too many variable factors depending on the earthing electrode installation method, excavation method, excavation area, and excavation length, etc., extensive and diverse review is necessary before work.
Especially if the measured earthing resistance is above the specified value, multiple earthing copper rods should be installed in parallel, and the ensuing increase in the scale of the excavation causes a lot of construction time and incurs a very large economic cost.
Moreover, the rectangular utility pole underbracing used in the aforementioned construction method is 1.2 m long, so a large area must be excavated in order to bury the underbracing in addition to the excavation done with the auger crane. Especially if two rectangular utility pole underbracings are to be installed in parallel or crossover, a large amount of the soil around the place where the utility pole is erected must be excavated.
Namely, even if utility pole construction work is done using an auger crane, the work cannot be finished until additional backhoe equipment or equivalent man power is used to bury the rectangular utility pole underbracing after erecting the utility pole. As a result, the quantity of construction becomes excessive due to complicated processes in utility pole underbracing construction, giving rise to a problem of taking a considerable amount of time for construction.
Accordingly, Korean Patent Application No. 2006-103273 filed by the present applicant discloses a construction method of rectangular utility pole underbracing which uses an extendable excavating unit for an auger crane that does not need additional excavation by dint of a 2-step bench cut by extension and reduction of an extendable excavating unit. According to this method, the excavation process is easy, the utility pole can be buried firmly with a small amount of earth during backfilling work, and work efficiency is increased.
In addition, relating to the aforementioned method, Korean Patent Application No. 2007-051211 filed by the present applicant discloses an excavation screw for an auger crane for mechanized excavation of burial holes for utility poles, or utility pole underbracing and guy wire underbracing. In the excavation screw of this patent, an extension rod is mounted such that it extends from the top of the excavation screw, oil inflow and discharge passages are formed inside the extension rod, and an extension unit having auxiliary excavating blades is combined to the bottom of the excavation screw. Inside the extension unit are formed main channels communicating with the oil inflow and discharge passages of the extension rod.
Since hydraulic pressure is also continuously acting on the auxiliary excavating blades of the lower extension unit corresponding to the varied excavation length of the extendable excavating screw, it is possible to properly use the extendable excavating screw with auxiliary excavating blades operated by hydraulic pressure according to the depth of excavation work. When using the extendable excavating screw with hydraulically extended auxiliary excavating blades, the construction period is shortened and workability is greatly improved.
In addition, Korean Patent Application No. 2006-0112100 filed by the present applicant discloses a semi-circular utility pole underbracing used in utility pole erection work. In this semi-circular utility pole underbracing, the earthing plate functioning as an earthing copper rod is monolithically attached to the utility pole underbracing in the course of carrying out the earthing work together with the utility pole erection work of overhead power transmission and distribution lines. In particular, friction-increasing concave slots and bolt inserting holes are formed on the outer surface of the utility pole underbracing, and the outer wall of the utility pole underbracing is semi-circular, and the inside surface has a utility pole gripping surface formed in an arch. For this semi-circular utility pole underbracing, an earthing plate of conductive metal material is made in a shape identical to the bottom surface of the semi-circular utility pole underbracing, and then the earthing plate is attached to the bottom surface of the utility pole underbracing, and an earthing terminal is formed on the outer surface of the earthing plate to connect the earthing plate and earthing terminal to each other. Therefore, without an additional excavation process for earthing work, earthing work is effectively carried out simultaneously with the utility pole underbracing mounting process, so the number of processes can be reduced innovatively, and the earthing effect is reliable and effective due to an increased earthing surface area.
And, Korean Patent Application No. 2007-0069477 filed by the present applicant discloses a hook for carriage and installation of a utility pole underbracing whereby the utility pole underbracing used in utility pole erection work for power distribution lines can be easily carried and installed. The hook for carriage and installation of this patent comprises a ring for hanging on the hook of the crane, a coupler positioned below the ring to level the utility pole underbracing, and a support for bearing the weight of the utility pole underbracing by combining the coupler and the utility pole underbracing. According to this patent, it is possible to hang the hook for carriage and installation on the crane, and the hook is easily fastened to the utility pole underbracing to easily move the utility pole underbracing to a desired position, and also since interference between the hook for carriage and installation and the utility pole underbracing is prevented, it is possible to mount the utility pole using a fastening means such as U bolt right away with the utility pole drawn near by the crane. Therefore, it is possible to quickly install with only one worker, and since the structure is relatively simple, it is possible to efficiently support and carry the utility pole underbracing, and since the utility pole underbracing is prevented from shaking or moving freely in transit, the work can be carried out very safely.
Meanwhile, Korean Patent Application No. 2007-009478 by the present applicant discloses a C-type utility pole underbracing with raised portions at both ends for construction of a utility pole. This patent relates to an arched utility pole underbracing supporting the lower end portion of a utility pole for firmly fixing the utility pole during utility pole erection and burial work. This arched utility pole underbracing has raised portions formed at both ends, and the arched rear portion of the underbracing has a smaller outer diameter than the front portion, and a hook inserting hole penetrates the central portion of the arched utility pole underbracing, and slit-shaped bolt combining holes are formed at a given interval on both sides of the inserting hole, so that mechanized work using the expander of an auger crane is possible during installation of the utility pole underbracing. Therefore, the grounding contact with the soil is improved through the raised portions at both ends, and also it is possible to aim at making the utility pole underbracing lightweight through the reduced rear portion. Also, transportation and installation of the utility pole underbracing is easy using a crane by dint of the hook inserting hole, and the U bolt can be easily fastened by dint of the bolt combining hole.